A radioimmunoassay for measuring PGE2 in human urine has been developed. In preliminary studies, hypertensive patients appear to have lower urinary PGE2 excretion, particularly those patients with low renin hypertension. The proposed investigation plans to confirm or refute these findings by additional studies in hypertensive patients. First, the urinary PGE material will be further identified and factors which may alter PGE excretion in normal subjects such as sex, urine volume and pH will be studied. Whether the lower PGE precedes or follows the hypertension will be investigated in humans by studying patients with remediable hypertension and in animals with experimental forms of hypertension. In view of the suggestion that renal PGE may influence renal function such as renal blood flow, water and sodium excretion and renin secretion, these factors will be investigated in subjects with low PGE excretion.